Polarizers used in liquid crystal display devices (LCDs) generally have a structure in which a polarizing film obtained by dyeing polyvinyl alcohol (PVA), etc., with iodine is sandwiched between two protective films. Triacetyl cellulose (TAC) films are commonly used as the protective films. Along with the recent trend of thinner LCDs, there is a demand for reducing the thickness of polarizers. However, when the thickness of TAC films used as protective films is reduced in order to satisfy this demand, problems such as insufficient mechanical strength and deteriorated moisture permeability occur. Moreover, TAC films are very expensive, and inexpensive alternative materials are strongly desired.
Accordingly, in order to reduce the thickness of polarizers, there is a proposal to use polyester films as protective films in place of TAC films, so that high durability can be maintained even though the thickness of the films is low (PTL 1 to PTL 3).